Liquid crystal display device and defect repairing method for the same

ABSTRACT

A liquid crystal display device comprises a pixel electrode, a thin film transistor, a gate line electrically coupled to the pixel through the thin film transistor and a first auxiliary layer having a first connecting portion overlapped with the pixel electrode and a second connecting portion overlapped with the gate line, wherein the pixel electrode is non-overlapped with the gate line and the first auxiliary layer is electrically insulated from the pixel electrode and the gate line. When a white defect occurs, the pixel electrode is electrically connected to the gate line through the first auxiliary layer thereby repairing the white defect as a black defect.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a liquid crystal display device, andmore particularly to a liquid crystal display device having a pixelrepairing structure.

2. Description of the Related Art

In the manufacturing process of a liquid crystal display (LCD) device,pixel defects are liable to be generated and should be repaired, whichcauses the manufacturing cost inevitably to be increased. Typically, thepixel defects are divided into white defects and dark defects, whereinthe white defects are easily recognized by naked eyes. Therefore, it ispreferable that the white defects should be repaired as black defects,which are always dark and not easily recognized by naked eyes.

One of conventional methods for repairing a white defect as a darkdefect is widely used in an LCD device 10 as shown in FIG. 1, in which apixel electrode 12 a has at least one part 13 overlapped with a gateline 14 to form a storage capacitor for enhancing the charge storingcapacity between the pixel electrode 12 a and a common electrode (notshown). When a white defect is caused by poor contact between the pixelelectrode 12 a and a switching element 16 or by malfunction of theswitching element 16, a short circuit is formed between the part 13 ofthe pixel electrode 12 a and the gate line 14 through a welding point 20formed by a laser such that the white defect can be repaired as a darkdefect. U.S. Pat. No. 6,882,375 B2 issued to Kim on Apr. 19, 2005discloses that a pixel electrode has a repair member overlapped with aneighboring front gate line.

In addition, some of conventional methods for repairing a white defectas a dark defect are used in an LCD device (not shown), in which a pixelelectrode is overlapped with a storage line (also referred to as storagecapacitor line) to form a storage capacitor.

U.S. Pat. No. 6,855,955 B2 issued to Jeon et al. (hereinafter Jeon) onFeb. 15, 2005 discloses that a pixel electrode is electrically connectedto a storage capacitor conductor through a contact hole, wherein thestorage capacitor conductor has a repairing portion overlapped with thegate line. When a white defect occurs, the gate line is short-circuitedwith the pixel electrode through the repair portion such that the whitedefect can be repaired as a dark defect.

However, in the above-mentioned conventional methods, at least oneconnecting portion (e.g. the part 13 in FIG. 1, the repair memberdisclosed by Kim and the repairing portion disclosed by Jeon)electrically connected to the pixel electrode is overlapped with thegate line such that a capacitor is formed between the connecting portionand the gate line and thus increases the capacitive load on the gateline. In particular, when the number of pixels along the gate line islarge, the capacitive load of the gate line may become considerable andthus cause the delay of the scan signal transmitted in the gate line.

SUMMARY OF THE INVENTION

The present invention provides a liquid crystal display device, whichcomprises a thin film transistor and a first auxiliary layer having afirst portion overlapped with a pixel electrode and a second portionoverlapped with a gate line, wherein the pixel electrode isnon-overlapped with the gate line and the first auxiliary layer iselectrically insulated from the pixel electrode and the gate line.

The present invention further provides a defect repairing method, whichis applied to the above-mentioned liquid crystal display device, whereinthe defect repairing method comprises a step of making the pixelelectrode electrically isolated from the thin film transistor, a step ofconnecting the first portion of the first auxiliary layer with the pixelelectrode and a step of connecting the second portion of the firstauxiliary layer with the gate line.

Furthermore, a second auxiliary layer is overlapped with the firstportion of the first auxiliary layer thereby facilitating the electricalconnection between the first portion and the pixel electrode.

According to the defect repairing method of the present invention, thepixel electrode can be electrically connected to the gate line throughthe first auxiliary layer thereby repairing a white defect as a blackdefect without signal delay problem caused by the capacitive load of thegate line.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present inventionwill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 shows a partial plan view of a conventional liquid crystaldisplay device.

FIG. 2 shows a partial plan view of a liquid crystal display deviceaccording to one embodiment of the present invention.

FIG. 3 shows a cross-sectional view taken along line A-A of FIG. 2 forillustrating the thin film transistor.

FIG. 4 shows a cross-sectional view taken along line B-B of FIG. 2 forillustrating the pixel repairing structure.

FIG. 5 shows a cross-sectional view taken along line A-A of FIG. 2 forillustrating the thin film transistor with its drain electrode andsource electrode being cut off by a laser.

FIG. 6 shows a cross-sectional view taken along line B-B of FIG. 2 forillustrating the pixel repairing structure, which has two welding pointsformed by a laser.

FIGS. 7A-7D are cross-sectional views for illustrating the method formaking the pixel repairing structure shown in FIG. 4.

FIG. 8 shows a partial plan view of a liquid crystal display deviceaccording to another embodiment of the present invention.

FIG. 9 shows an equivalent circuit of the liquid crystal display devicesshown in FIGS. 2 and 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 2 shows a partial plan view of a liquid crystal display device 100according to one embodiment of the present invention. The liquid crystaldisplay device 100 comprises a plurality of pixel regions 102, aplurality of data lines 104, a plurality of gate lines 106, a pluralityof storage capacitor lines 107, and a plurality of thin film transistors108. In FIG. 2, the gate lines 106 and storage capacitor lines 107 aredenoted by the dotted lines and formed on a substrate (not shown).

The plurality of pixel regions 102 are arranged in rows and columns toform a matrix, and each pixel region 102 has a pixel electrode 110 and apixel repairing structure 111 formed thereon. The data line 104 iselectrically coupled, through all the thin film transistors 108 at thesame column, to all the pixel electrodes 110 of the pixel regions 102arranged in the same column. The gate line 106 is electrically coupled,through all the thin film transistors 108 in the same row, to all thepixel electrodes 110 of the pixel regions 102 arranged in the same row.The storage capacitor line 107 is formed across the pixel regions 102arranged in a row and overlapped with the pixel electrodes 110 to form astorage capacitor for enhancing the charge storing capacity between thepixel electrode 110 and a common electrode formed on a counter substrate(not shown) facing the above-mentioned substrate. In the other word, thestorage capacitor line 107 is electrically insulated from the pixelelectrodes 110 and data lines 104. The thin film transistor 108 isformed close to the intersection of the data line 104 and the gate line106. The thin film transistor 108 has a source electrode 108 aelectrically connected to the data line 104, a drain electrode 108 belectrically connected to the pixel electrode 110 through a contact hole109. In this embodiment, the source electrode 108 a and the drainelectrode 108 b are partially overlapped with a section 106 a of thegate line 106 so that the section 106 a of the gate line 106 canfunction as a gate electrode of the thin film transistor 108. Inaddition, it should be noted that the terms “source electrode” and“drain electrode” could be alternatively used in accordance with thedirection of the current flow in the thin film transistor 108.

FIG. 3 shows a cross-sectional view taken along line A-A of FIG. 2 forillustrating the thin film transistor 108. The thin film transistor 108has the gate electrode, i.e. the section 106 a of the gate line 106,formed on a substrate 112. A gate insulating layer 114 is formed tocover the section 106 a of the gate line 106. A semiconductor layer 116is formed on the gate insulating layer 114 and overlapped with thesection 106 a of the gate line 106. The source electrode 108 a and thedrain electrode 108 b are formed on the gate insulating layer 114 withparts of them covering the semiconductor layer 116. A protective layer118 is formed on the gate insulating layer 114 to cover the sourceelectrode 108 a, the drain electrode 108 b, and parts of thesemiconductor layer 116. The pixel electrode 110 is formed on theprotective layer 118 and electrically connected to the drain electrode108 b through the contact hole 109 formed in the protective layer 118.

Referring to FIG. 3, the thin film transistor 108 has a predeterminedchannel formed between the source electrode 108 a and the drainelectrode 108 b on the semiconductor layer 116. When the gate line 106receives a scan signal, it transmits the scan signal to the section 106a, i.e. the gate electrode of the thin film transistor 108, forswitching on/off the predetermined channel of the thin film transistor108. In addition, when the section 106 a of the gate line 106 is appliedwith the scan signal, the source electrode 108 a can receive a datasignal from the data line 104 and then transfer the data signal to thedrain electrode 108 b through the predetermined channel. Afterward, thedata signal can be applied to the pixel electrode 110 by the drainelectrode 108 b such that a potential difference can be generatedbetween the pixel electrode 110 and the common electrode formed on thecounter substrate (not shown) facing the substrate 112 for rotating theliquid crystal (not shown) within a pixel cell, and then form a desiredpicture. The pixel cell described in this embodiment is the basic unitto form a color, e.g. one of the red, green and blue.

FIG. 4 shows a cross-sectional view taken along line B-B of FIG. 2 forillustrating the pixel repairing structure 111. In this embodiment, thepixel repairing structure 111 is formed to repair a defective pixel andincludes a first auxiliary layer 120 and a second auxiliary layer 122.The first auxiliary layer 120 is formed on the gate insulating layer 114and covered with the protective layer 118 such that it can beelectrically insulated from the gate line 106, the second auxiliarylayer 122 and the pixel electrode 110. The first auxiliary layer 120 hasa connecting portion 120 a overlapped with the gate line 106, and aconnecting portion 120 b overlapped with the pixel electrode 110. Thesecond auxiliary layer 122 as a dummy layer is formed on the substrate112, electrically isolated from the gate line 106, and covered with thegate insulating layer 114. In more detail, the second auxiliary layer122 is overlapped with the connecting portion 120 b of the firstauxiliary layer 120 and electrically insulated from the first auxiliarylayer 120 and the pixel electrode 110. In the other word, the secondauxiliary layer 122 is an electrically insulated island. Furthermore, innormal pixel regions 102, the pixel repairing structure 111 iselectrically insulated with surroundings, such as the gate lines 106,the data lines 104, the thin film transistors 108, the pixel electrodes110 and the storage capacitor lines 107.

Now referring to FIGS. 2 to 4, if a defect occurs at the predeterminedchannel in one of the thin film transistors 108, e.g. the thin filmtransistor also denoted by the numeral 208 shown in FIG. 2, then thepixel electrode 210 electrically connected to the thin film transistor208 is defective, so that the pixel cell formed by the pixel electrode210 becomes a bright dot, i.e. a white defect. The defect repairingmethod of the present invention for repairing such a defective pixelcell will be described below.

In this embodiment, it is assumed that the pixel electrode also denotedby the numeral 210 is found defective and causes a bright dot. In orderto repair the white defect, firstly, the electrical path between thepixel electrode 210 and the drain electrode 108 b of the thin filmtransistor 208 should be cut off such that the pixel electrode 210 canbe electrically isolated from the drain electrode 108 b. The electricalpath can be cut by using a laser to cut off the connecting part 113 ofthe drain electrode 108 b and the connecting part 115 of the sourceelectrode 108 a as shown in FIG. 5, such that the pixel electrode 210 iselectrically isolated from the thin film transistor 208.

Now referring to FIGS. 2 and 4, after the above cutting step isimplemented, an electrical path between the pixel electrode 210 and thegate line 106 is then created such that the pixel electrode 210 can berepaired as a dark dot, i.e. black defect. The electrical path can becreated by using the laser to form two welding points 124 a and 124 b inthe pixel repairing structure 111 as shown in FIG. 6. The welding point124 a is formed by welding the connecting portion 120 a of the firstauxiliary layer 120 with the gate line 106. The welding point 124 bcould be formed by two methods: one is to weld the connecting portion120 b of the first auxiliary layer 120 with the pixel electrode 210, andthe other is further to weld the second auxiliary layer 122 with theconnecting portion 120 b and the pixel electrode 210 for facilitatingthe electrical connection between the connecting portion 120 b and thepixel electrode 210. When the two welding points 124 a and 124 b areformed by the laser, the pixel electrode 210 can be electricallyconnected to the gate line 106 through the first auxiliary layer 120.Accordingly, the pixel electrode 210 can be applied with a potentialgenerated from the gate line 106 so that the defective pixel cell can berepaired and displayed as a dark dot.

FIGS. 7A-7D are cross-sectional views for illustrating the method formaking the pixel repairing structure 111 shown in FIG. 4. A method formaking the liquid crystal display device 100 will be described belowwith reference to FIGS. 2, 3 and 7A-7D.

Referring to FIGS. 2, 3 and 7A, a gate line 106, a gate line section 106a, a storage capacitor line 107 and a second auxiliary layer 122 areformed on a substrate 112. The gate line 106, the gate line section 106a, the storage capacitor line 107 and the second auxiliary layer 122 areformed by depositing at least one metal layer, e.g. aluminum (Al),copper (Cu), chromium (Cr), silver (Ag), gold (Au), molybdenum (Mo) orany other metal layer or any stacked metal layer, through a sputteringtechnique or other techniques, and then patterning it with a first mask.

Referring to FIGS. 2, 3 and 7B, a gate insulating layer 114 is formed onthe substrate 112 to cover the gate line 106, the gate line section 106a, the storage capacitor line 107 and the second auxiliary layer 122.The gate insulating layer 114 can be formed of at least one insulatingmaterial, e.g. silicon nitride (SiNx), silicon oxide (SiOx), or stackedthereof or any other such material or any other transparent material.Afterward, a semiconductor layer 116 is formed on the gate insulatinglayer 114 and overlapped with the gate line section 106 a. Thesemiconductor layer 116 is formed by depositing a semiconductormaterial, e.g. amorphous silicon, on the gate insulating layer 114 andthen patterning it with a second mask.

Referring to FIGS. 2, 3 and 7C, a data line 104, a source electrode 108aconnected to the data line 104, a drain electrode 108 b and a firstauxiliary layer 120 are formed on the gate insulating layer 114.Further, the source electrode 108 a and the drain electrode 108 b areformed on the gate insulating layer 114 with parts of them covering thesemiconductor layer 116. The data line 104, the source electrode 108 a,the drain electrode 108 b and the first auxiliary layer 120 are formedby entirely depositing at least one metal layer, e.g. magnesium (Mg),calcium (Ca), aluminum (Al), Barium (Ba), lithium (Li), silver (Ag),gold (Au) or any other metal layer or any stacked metal layer, through aCVD technique or a sputtering technique, and then patterning it with athird mask. Afterward, a protective layer 118 is formed on the gateinsulating layer 114 to cover the data line 104, the source electrode108 a, the drain electrode 108 b, parts of the semiconductor layer 116and the first auxiliary layer 120.

Referring to FIGS. 2 and 3, the protective layer 118 is patterned with afourth mask to form a contact hole 109 such that a part of the drainelectrode 108 b is exposed from the contact hole 109.

Referring to FIGS. 2, 3 and 7D, a pixel electrode 110 is formed on theprotective layer 118 without overlapping with the gate line 106. Inaddition, the pixel electrode 110 is further formed into the contacthole 109 so as to be electrically connected to the drain electrode 108b. The pixel electrode 110 is formed by depositing at least onetransparent conductive material, e.g. indium tin oxide (ITO), indiumzinc oxide (IZO), indium oxide (10), tin oxide (TO), zinc oxide (ZO),aluminum zinc oxide (AZO) or any other transparent conductive layer orany stacked conductive layer, on the protective layer 118, and thenpatterning it with a fifth mask.

According to the method for making the liquid crystal display device100, the pixel repairing structure 111, together with the thin filmtransistor 108, is formed using the same masks and patterning processes.For example, the second auxiliary layer 122, together with the gate line106, is formed on the substrate 112 through the same mask, i.e. thefirst mask, and the same patterning process. In addition, the firstauxiliary layer 120, together with the data line 104, the sourceelectrode 108 a and the drain electrode 108 b, is formed on the gateinsulating layer 114 through the same mask, i.e. the third mask, and thesame patterning process. Therefore, the pixel repairing structure 111can be formed without using any additional mask and patterning process.

In the pixel repairing structure 111 shown in FIG. 4, the secondauxiliary layer 122 is formed to facilitate the formation of the weldingpoint 124 b shown in FIG. 6 for the electrical connection between theconnecting portion 120 b and the pixel electrode 110. Therefore, itshould be understood that the second auxiliary layer 122 can beoptionally formed in the liquid crystal display device 100.

FIG. 8 shows a partial plan view of a liquid crystal display device 200according to another embodiment of the present invention. In FIG. 8,elements having the same functions as in the embodiment of FIG. 2 aredenoted by the same numerals. The liquid crystal display device 200 issubstantially the same with the liquid crystal display device 100 shownin FIG. 2 except that a first auxiliary layer 220 and a second auxiliarylayer 222 are formed at the bottom edge of the pixel electrode 210rather than the top edge of the pixel electrode 210 at which the firstauxiliary layer 120 and the second auxiliary layer 122 shown in FIG. 2are formed. In the other word, the first auxiliary layer 220 and thethin film transistor 108, 208 are overlapping the same pixel electrode110, 210 and the gate line 106. In addition, the first auxiliary layer220 has a connecting portion 220 a overlapped with the gate line 106,which is coupled to the pixel electrode 110, 210 through the thin filmtransistor 208. The first auxiliary layer 220 further has a connectingportion 220 b overlapped with the pixel electrode 110, 210 and thesecond auxiliary layer 222. Similarly, when a white defect occurs, theelectrical path between the pixel electrode 210 and the drain electrode108 b of the thin film transistor 208 should be firstly cut off by alaser such that the pixel electrode 210 is made electrically isolatedfrom the thin film transistor 208. Secondly, the pixel electrode 210 canbe electrically connected to the gate line 106 by welding the connectingportion 220 a of the first auxiliary layer 220 with the gate line 106,and welding the connecting portion 220 b of the first auxiliary layer220 with the pixel electrode 210 or welding the connecting portion 220 bof the first auxiliary layer 220 with the pixel electrode 210 and thesecond auxiliary layer 222. Therefore, the white defect can be repairedas a black defect.

FIG. 9 shows an equivalent circuit of the liquid crystal display deviceshown in FIGS. 2 and 8. As shown in FIG. 9, the thin film transistor 108has a capacitor Cgs formed between the gate electrode 106 a and thesource electrode 108 a, and a capacitor Cgs formed between the gateelectrode 106 a and the drain electrode 108 b. A liquid crystalcapacitor C_(Lc) is formed between the pixel electrode 110 and a commonelectrode (not shown) having a common voltage Vcom. When the thin filmtransistor 108 is turned on, a voltage received from the data line 104can be transferred to the pixel electrode 110 and then held in theliquid crystal capacitor C_(LC) transitionally. Therefore, the voltageheld in the liquid crystal capacitor C_(LC) can be applied to the liquidcrystal (not shown). In addition, a storage capacitor Cst is also formedbetween the pixel electrode 110 and the common electrode for enhancingthe charge storing capacity of the liquid crystal capacitor C_(LC).

In the liquid crystal display devices 100 and 200 shown in FIGS. 2 and8, the pixel electrode 110 is formed without overlapping with the twoadjacent lines 106, that is, the pixel electrode 110 is non-overlappedwith the two adjacent gate lines 106. In addition, both of the firstauxiliary layers 120 and 220 are electrically insulated from the pixelelectrode 110, 210 and the two adjacent gate lines 106. Therefore, eachgate line 106 is free of capacitive load caused by the pixel electrode110, 210 or any connecting portion electrically connected to the pixelelectrode 110, 210 as shown in FIG. 9 such that the scan signaltransmitted thereof will not be delayed.

Although the invention has been explained in relation to its preferredembodiment, it is not used to limit the invention. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the invention as hereinafter claimed.

1. A liquid crystal display device, comprising: a first gate line fortransmitting a first scan signal; a second gate line next to the firstgate line; a pixel electrode formed without overlapping with the firstgate line and the second gate line; a thin film transistor having afirst electrode electrically connected to the pixel electrode, a secondelectrode for receiving a data signal, and a gate electrode forreceiving the first scan signal; and a first auxiliary layer having afirst connecting portion overlapped with the pixel electrode and asecond connecting portion overlapped with one of the first gate line andthe second gate line; wherein the first auxiliary layer is electricallyinsulated from the pixel electrode, the first gate line and the secondgate line.
 2. The liquid crystal display device as claimed in claim 1,wherein the pixel electrode is located between the first gate line andthe second gate line.
 3. The liquid crystal display device as claimed inclaim 1, wherein the first auxiliary layer, the first electrode and thesecond electrode are formed by same manufacturing processes.
 4. Theliquid crystal display device as claimed in claim 1, further comprising:a second auxiliary layer overlapped with and electrically insulated fromthe first connecting portion of the first auxiliary layer.
 5. The liquidcrystal display device as claimed in claim 4, wherein the secondauxiliary layer, the first gate line and the second gate line are formedby same manufacturing processes.
 6. The liquid crystal display device asclaimed in claim 4, wherein the second auxiliary layer is electricallyisolated from the first and second gate lines and electrically insulatedfrom the pixel electrode.
 7. The liquid crystal display device asclaimed in claim 1, further comprising: a gate insulating layer coveringthe first and second gate lines, wherein the first electrode, the secondelectrode and the first auxiliary layer are formed on the gateinsulating layer; and a protective layer covering the first electrode,the second electrode and the first auxiliary layer, wherein the pixelelectrode is formed on the protective layer.
 8. The liquid crystaldisplay device as claimed in claim 7, further comprising: asemiconductor layer formed on the gate insulating layer, wherein a partof the first electrode and a part of the second electrode are formed onthe semiconductor layer.
 9. A defect repairing method, applied to theliquid crystal display device of claim 1 while the pixel electrode isdefective, comprising: connecting the first connecting portion of thefirst auxiliary layer with the pixel electrode; and connecting thesecond connecting portion of the first auxiliary layer with the one ofthe first gate line and the second gate line.
 10. The defect repairingmethod as claimed in claim 9, further comprising: making the pixelelectrode electrically isolated from the thin film transistor.
 11. Thedefect repairing method as claimed in claim 10, wherein the making stepis implemented by cutting off the electrical path between the pixelelectrode and the thin film transistor.
 12. The defect repairing methodas claimed in claim 9, wherein the two connecting steps are implementedby a laser.
 13. The defect repairing method as claimed in claim 9,wherein the liquid crystal display device further comprises a secondauxiliary layer overlapped with the first connecting portion of thefirst auxiliary layer, and wherein the step of connecting the firstconnecting portion of the first auxiliary layer with the pixel electrodefurther comprises: connecting the first connecting portion of the firstauxiliary layer with the second auxiliary layer.
 14. The defectrepairing method as claimed in claim 13, wherein the connecting stepsare implemented by a laser.
 15. A pixel repairing structure for a liquidcrystal display device having a first gate line and a pixel electrodeadjacent to the first gate line, comprising: a first auxiliary layerhaving a first portion overlapped with the pixel electrode and a secondportion overlapped with the first gate line; and a second auxiliarylayer overlapped with the first portion of the first auxiliary layer;wherein the first auxiliary layer is electrically insulated from thepixel electrode, the first gate line and the second auxiliary layer. 16.The pixel repairing structure as claimed in claim 15, furthercomprising: a second gate line next to the first gate line such that thepixel electrode is located between the first gate line and the secondgate line.
 17. The pixel repairing structure as claimed in claim 16,wherein the second auxiliary layer is electrically isolated from thefirst and second gate lines and electrically insulated from the pixelelectrode.
 18. The pixel repairing structure as claimed in claim 16,wherein the second auxiliary layer, the first gate line and the secondgate line are formed by same manufacturing processes.
 19. The pixelrepairing structure as claimed in claim 15, wherein the second auxiliarylayer is electrically isolated from the first gate line and electricallyinsulated from the pixel electrode.
 20. The pixel repairing structure asclaimed in claim 15, further comprising: a gate insulating layercovering the first gate line and the second auxiliary layer, wherein thefirst auxiliary layer is formed on the gate insulating layer; and aprotective layer covering the first auxiliary layer, wherein the pixelelectrode is formed on the protective layer.